Paper360 - January/February 2010 - (Page 35)

ONLINE TOOLS TECHLINK Tracking TENSION A NEW ONLINE NIP LOAD and tension profile analysis tool BOB BETTENDORF and TATU PITKÄNEN M etso’s portable iRoll technology is a new online analysis tool that provides precise information about CD and MD tension profile variations and nip load profiles, for all paper and board grades. The iRoll sensors are taped onto a roll surface, and a signal-processing module with a transmitter is attached to the roll head or shaft. A complete CD profile is generated with each revolution of the roll and the measured profile information is transmitted over a wireless link to a receiver and on to a PC for analysis. MILL PROVEN A mill producing high quality woodfree coated paper had a constant problem with web shifting in their off-machine coater. The lateral movement caused web breaks, especially during splicing, and also created difficulties in web edge cutting. Over time, the speed of the line was increased and the web shifting caused production bottlenecks. Also, the line was less efficient than it could have been which increased production costs and indirectly led to higher energy consumption. For years, the reason for the web shift had been a mystery. A variety of modifications to the line attempted to fix the problem, but none was effective. It was assumed that a tension profile variation was the reason for the web shifting, so several portable iRoll systems were installed along the line to separately identify how each sub-process affected the web profile. The papermaking line was equipped with tension profile sensors, roll nip load profile sensors, and web edge sensors to measure web shift. The first observation was that the off-machine coater web shifting had a direct correlation with the skewness of the tension profile measured at the coater. The skewness was quantified by fitting a straight line to each measured tension profile and calculating an angular coefficient of the line. These coefficients were recorded for each paper roll and compared with the measured edge position of the web. In this manner, it was demonstrated that the skewed tension profile was causing the web to shift. However, the cause of the tension profile skewing needed to be determined. Tension profiles measured at the paper machine did not correlate with the tension profile at the coater. This surprised the analysis team as it was initially expected that the tension profile variations would come from the wet end. However, as this was not the case, the paper machine, and all its sub-processes, were eliminated as a cause of the problem. Next, it was found that the tension and roll profiles at the rereeler had quite good correlation to the coater tension profiles. This narrowed the search for the cause of the tension profile varia- tion, to either the rereeler or the paper machine reel. To further narrow the search, the nip load profile at the paper machine reel was examined which revealed that these nip profiles had excellent correlation to the tension profile at the coater. Because the paper machine reel was the first place along the line where this correlation was found, it had to be the root cause of the web shifting. The analysis team concluded that the wound on tension (WOT) profile of each parent roll was skewed and the amount of skew also changed during reeling. When the rolls with variations were unwound at the coater, the web shifting occurred. The nip load controls of the reel were updated and adjusted to have a uniform WOT Profile. Also, the reeling recipes were adjusted to create a better roll structure. After the reel control system was modified, the tension profile changes at the coater were reduced significantly. The web behavior was stable and web shifting no longer occurred. Bob Bettendorf is Application Engineer and Tatu Pitkänen is R&D Project Manager at Metso Paper. They can be reached at and Paper360º January/February 2010

Table of Contents for the Digital Edition of Paper360 - January/February 2010

Paper360 - January/February 2010
Over the Wire
Outlook: North America 2010
Confronting the Carbon Challenge
Improve Your Energy Efficiency
Feature: Paper Machine Clothing
Around the Industry
Association News
Improving Print Performance
Tracking Tension
Dateline: London
Index of Advertisers

Paper360 - January/February 2010